: whats a good manifold for a 425

05-19-04, 01:14 PM

I just learned that my stock 425 only has 180 horse power but it does have 320 ft lbs of tourqe. I have read a few threds on the site and have come to the realization that the stock manifold sits to low. could any one tell me where I can get a manifold that I can still bolt my a/c to and the factory carb but gain some good HP. or would it be better to just have a machine shop pollish and port the stock manifold.

05-19-04, 11:58 PM
Unfortunately, aftermarket manifolds do not provide a way to retain the stock A/C compressor. However if you get a bracket from Vintage Air, you can use the newer style GM compressor, and still have working A/C.

Angela Desmond
05-21-04, 11:21 AM
opening up the intake runners won't help much because it's the shape of the runners leading the A/F mixture down, then up and down again to get into the intake ports that kills any performance from this manifold. the shape of the runners also makes it very difficult to get any size mandrel attached to a die grinder in there. Polishing isn't a good idea on the intake side ,neither manifold or intake ports because a slightly rough finish, like finishing the porting with 120 grit, is better for fuel atomization. David Vizard has written much about this subject. Save the polished finish for the exhaust side...